Field of the Invention
The present invention relates to a combined oil ring, and, more particularly, to a three-piece combined oil ring including a pair of upper and lower side rails and a spacer expander arranged therebetween.
Description of the Related Art
Oil rings that have been known up to now scrape extra engine oil attached to a cylinder inner wall surface of an internal combustion engine, and form a proper oil film, to thereby prevent a piston from being seizure along with an operation of the internal combustion engine. Various forms have been known for such oil rings. For example, Japanese Patent Laid-Open No. 2011-185383 describes a combined oil ring including a pair of upper and lower side rails and a spacer expander arranged therebetween. The spacer expander includes: a large number of upper pieces and lower pieces that are alternately arranged in a circumferential direction so as to be spaced apart in an axial direction and the circumferential direction; coupling pieces that respectively couple the adjacent upper pieces and lower pieces; and ear parts that are each formed so as to erect in an inner circumferential end portion of each of the upper pieces and the lower pieces, and serve to push the side rails.
As described above, combined oil rings scrape extra engine oil attached to a cylinder inner wall surface of an internal combustion engine, and form a proper oil film, to thereby prevent a piston from being seizure. Unfortunately, such combined oil rings have a problem that carbon sludge and the like generated from unburned carbon and lubricant combustion products are deposited between the spacer expander and the side rails, and hinder smooth scraping of the engine oil.
In order to solve this problem, for example, in the combined oil ring described in Japanese Patent Laid-Open No. 2011-185383, at least one of an upper surface of each upper piece and a lower surface of each lower piece has a groove formed thereon, and each ear part has, formed therein, a through-hole with which the groove is communicated. The scraped engine oil flows out through the groove and the through-hole, and hence carbon sludge is prevented from being deposited between the spacer expander and the side rails.
In conventional combined oil rings, a size thereof in an axial direction is made smaller to reduce tension, in response to a demand for smaller friction. Unfortunately, along with passage of operating time of the internal combustion engine, carbon sludge is likely to be deposited between the spacer expander and the side rails. In particular, carbon sludge is likely to be deposited in a narrowest portion in a space between the side rails and the spacer expander or in corner parts 100 in which side rails 11′ and a spacer expander 12′ are in contact with each other as illustrated in FIG. 6. Hence, the conventional combined oil rings still have a problem that, if the internal combustion engine is operated for a long period of time, carbon sludge is gradually deposited in these portions, and hinders the engine oil from smoothly flowing out. Japanese Patent Laid-Open No. 2011-185383 does not describe specific numerical values for dimensions of the oil ring, and hence optimal dimensions and shape for solving the above-mentioned problem are required.